Field of the Invention
The present invention relates to an installation and a method for rolling a metal strip. The installation includes a rolling mill in which the strip is rolled in continuous movement, rolling agents brought into contact with rolls of the rolling mill and with the strip, a strip traction unit positioned at the output of the rolling mill, and a decontamination module with at least one degreasing means positioned between the output of the rolling mill and the traction unit so as to remove residual agents from the strip at the output of the rolling mill.
Installations for rolling metal strip, in particular cold rolling, that are able to roll strips made primarily of stainless steel, require the use of a high-capacity rolling mill (>400,000 tons per year) such as a tandem mill. Rolling is carried out continuously (i.e. the strip is in continuous movement) to limit the costly loss of time and material caused by inserting and releasing the strip, as required in a non-continuous rolling mill. Upstream of the rolling mill, the use of a welder makes it possible to join successive strip tails and heads together in an uncoiling section provided by at least one uncoiler. Downstream of the rolling mill or at least at the end of a complete rolling line, it is ultimately necessary to separate these strips to wind them onto different coils using at least one coiler.
The surface condition of the strip is a critical element in strip quality throughout the rolling line, on account of which frequent visual inspections are often required.
Rolling installations such as tandem rolling installations (designed for carbon- and stainless-steel strips) are preferably fitted with dual coilers, positioned at the downstream outlet of the rolling mill and downstream of shears used to cut the strip, preferably on the fly, and separate same to form separate strips which are then coiled alternately onto two mandrels, exerting a suitable degree of traction on the strip upstream of the coiling in consideration of the conditions required for good coiling, good coil performance once off the coiler mandrel and subsequent uncoiling stresses on the multi-operation lines downstream of the rolling operation. The strip traction required for coiling is usually different from that required for rolling. The strip traction related to rolling is usually greater or much greater than the strip traction required for coiling. During cutting and transfer of the head of a strip to the related coiler, traction is usually only provided or permitted using a traction unit such as a pinch roll able to establish less traction than the strip traction required at the rolling-mill output for good rolling conditions, which may result in a disturbance in the strip thickness and generation of a final product that is out of tolerance and therefore downgraded and often unusable, which is very costly in particular in the case of stainless steel production. Equally, the strip rolling speed at the output of the rolling mill has to be reduced during operations downstream of the output of the rolling mill, in particular when cutting the strip (shearing, start of coiling on a mandrel, insertion of paper strip between coil windings when producing stainless steel, inspection, etc.), which results in a significant loss of productivity and impacts quality factors relating to the rolling method, which leads to faults in the thickness and flatness of the strip after rolling and in general all well-known quality issues caused by transient states relating to speed variations and/or low speeds. In the field of stainless steel strips, inserting a paper sheet or film between the windings of the resulting coils requires a very low transfer/insertion speed, for example around 30 to 60 m/min and/or the use of complex and costly machinery to insert this sheet on the fly at a speed of for example 60 to 100 m/min.
This speed reduction results in a loss of rolling productivity and an increase in rolling stress, which may negatively impact the parameters of the rolled product outputted.
A rolling installation belonging to Nisshin Steel Company Limited (publication GB1313577) has been described, disclosing a tandem rolling mill for continuous production of stainless steel strip. The tandem rolling mill is provided with successive rolling stands (20 high) that require longer, non-automated roll change times, as well as “double pinch” bridle rolls upstream and downstream of the rolling mill which may cause surface, thickness or flatness defects on the strip. This installation is however a good starting example for the present invention, inasmuch as it describes a rolling installation for a metal strip comprising at least:                a rolling mill in which the strip is rolled in continuous movement,        a strip traction unit positioned at the output of the rolling mill.        
It should be noted that the present invention also takes into account lubrication and cooling means inside the rolling mill (on the rolling mill rolls and therefore on the strip) in order to guarantee a predetermined coiling, compression and sliding ratio of the strip between the rolls beneath the strip contact arc on the rolling rolls. This makes it possible to obtain a lubrication/cooling rate that is usable for rolling in the rolling mill, firstly to cool the rolled strip and secondly to achieve, under good conditions and under rolling stresses, a desirable ratio between the coiling, compression and sliding of the strip moving through the rolling mill.
At the output of the rolling mill, the surface of the strip retains residual rolling agents such as traces of oil and other strip and roll liquid spray elements used in the rolling process, as well as grease from miscellaneous possible sources. The presence of oil or other greasy substances on the strip makes it difficult to exert significant traction stresses on the strip coming out of the rolling mill for good rolling conditions. Since traction is generated by a traction unit at the output of the rolling mill, such as bridle rolls and/or pinch rolls, these traction elements are necessarily coated with oil, other greasy substances or other residues, which definitively reduces the friction ratio and adherence required to exert traction on the strip. Furthermore, slipping causes and facilitates lateral deviations of the strip along the route of same up to the coiler (for example in an accumulator at the output of the rolling mill and/or on the coiler), which reduces productivity. In this case, means are required to prevent and correct these strip position deviations which result in a real loss of control of the strip movement characteristics, such as loss of traction, accumulation and/or coiling precision, in particular on the fields of the coils. Oil, other greasy substances and other residues remaining on the surface of the strip coming out of the rolling mill are also contaminants, affecting the final cleanliness of the strip, adversely affecting the end quality of same and adversely affecting the mechanical and clean conservation properties of the paper strip required for strip coiling in the specific case of stainless strips to be coiled.